350Z_Al

My car is an 03 Track w/ 44k miles. Mods were done in the following order:

-Test Pipes
-Pop Charger
-Plenum Spacer

Since doing the plenum spacer I have had an occasional rough idle. If the car sits idling for more than about 30 seconds after being warmed up the idle kicks down to in the 500rpm range (from my MAC Tools scanner) and it idles rough as hell with a misfire. It will occasionally throw the P0300 random misfire code.

Now, after doing some reading I have found that this can be caused by a few things like a vacuum leak or electrical issues. Now, with an idle down in the 500 range I don't think it could be a vacuum leak. The car runs great and only has that misfire at low idle so I don't suspect any electrical issues.

I have read other people having this code when they do a plenum spacer and test pipes. My understanding it is a lean misfire causing this code to appear. Is this something I just have to live with? I guess down the road if I go with a UTEC I can tune out this lean condition at idle?

Am I risking anything driving the car with the CEL on, or having that misfire at idle happening?

coachk

iTrader: (21)

Do you have a wideband gauge to see what your A/F and vacuum is at. From the looks of the mods you did, probably need a re tune.

gabez33

iTrader: (7)

by any chance did you unplug a harness from the rear(behind, underneath the plenum) when you installed the plenum spacer??

mw9

iTrader: (51)

keep me up to date, i have the same mods on an 03 an are having the same problems

3hree5ive0ero

iTrader: (95)

I have the above listed mods plus a couple more. I've had this code a couple of times, but after I reset the ECU (the ignition method), it went away. It came back a couple of more times, but I'd reset it every time it came back and everything was back to normal. That was about a year and a half ago and after 3 times of throwing that exact same code, it hasn't come back.

My suggestion is to reset your ECU and see if it returns. If it does, try resetting again. If it does come back again, then I'd seek professional help.

350Z_Al

The code is not an "all the time code" it only comes on occasionally after the car idles for long periods of time. If I clear it, it will go away for a while then come back...

I think I'm only seeing it now because it is winter and I let the car warm up for a few minutes before driving (so the car spends more time idling than normal). I did the mods about two months before winter and did not see the code until just recently.

snuffy11

I just installed a z1 plenum spacer along with a jwt popcharger and I too am getting a rough idle after engine warm up.. Have not seen the engine light come on but , was worried about whether to reflash the ecu or not..

BrazenZ

Those 3 mods by themselves should'nt cause a PO300 CEL, You also stated that your car is idling lower. You can raise the idle with cipher software and that might make the cel go away. I bet that the Cel plus the fact your engine is idling lower means you have a vacuum leak.

I'm curious why you think that because your car idles at 500 rpms ( mine idled about 700 when it was completely stock with A/C off) that you can't have a vacuum leak? The lower idle is misfire is most likely tripping the random misfire cel.

Check the 5/8 vacuum hose on the passenger side plenum. After removing the hose from the plenum it keep leaking until I sealed it with gasket adhesive. If that's not the problem spray WD-40 around your plenum and not around the air filter ( becareful the stuff is very flammable) If while your spraying around the plenum your car starts idling faster, then you have a vacuum leak. If you know mechanic of have a friend with a smoke machine that is a better way to check for vacuum leaks.

Finally, No driving around with a low idle misfire will not cause any serious damage to your engine. I have seen some pretty radical mods to the VQ engine and it has been my experience that with a little detective work the PO300 cel can be cleared unless you have extremely radical aftermarket camshafts.

rcdash

iTrader: (18)

hmmm, how about changing them plugs since I figure they have a little something to do with misfires?

350Z_Al

Thanks, very informative post!

From previous experience, vacuum leak = high idle.. That's why I though that...

I'm thinking it may be a vacuum leak as the rough idle happened right after installing the plenum spacer...... I'll look into that when it warms up, it's currently about -20*F outside

TTwinTTurbo

Wow this is exactly the same damn problem I am having. And I just installed the spacer. I got a check engine light..did the reset method and its gone..but the idling is still rough. If it sets at idle too long after warmup it will drop really low and sound like its misfiring. I guess that its just something that we have to deal with?